1. Field of the Invention
The present invention relates to a liquid crystal projector.
2. Description of the Prior Art
A liquid crystal panel, a light source lamp for backlight arranged on a rear surface of the liquid crystal panel, a signal processing circuit, and a power supply circuit are provided in a casing of a liquid crystal projector. Further, a plurality of cooling fans for cooling the liquid crystal panel, the light source lamp for backlight, and so forth are provided in the casing of the liquid crystal projector.
FIG. 1 illustrates the schematic configuration of the liquid crystal projector.
The liquid crystal projector comprises an operation unit 1, a main control unit 2, a display unit 3, a storage unit 4, and a fan control unit 5. Three temperature sensors 11, 12, and 13 are connected to the main control unit 2. Five cooling fans 6 are connected to the fan control unit 5.
The first temperature sensor 11 is for measuring the ambient temperature of the main body of the liquid crystal projector (room temperature). The first temperature sensor 11 is arranged in the vicinity of a place which is not affected as greatly as possible by the inside of the main body of the liquid crystal projector and is correlated with the room temperature, for example, an air suction port inside the main body of the liquid crystal projector.
The second temperature sensor 12 is for measuring the ambient temperature of a liquid crystal panel, and is arranged inside the main body of the liquid crystal projector and around the liquid crystal panel.
The third temperature sensor 13 is for measuring the ambient temperature of a light source lamp for backlight and is arranged inside the main body of the liquid crystal projector and around the light source lamp for backlight.
As shown in FIG. 2, the main control unit 2 controls the cooling fan 6 in response to a temperature T11 sensed by the first temperature sensor 11 (room temperature). That is, when it is judged that the room temperature is not more than a predetermined temperature T1 by the temperature T11 sensed by the first temperature sensor 11, the voltage of the cooling fan 6 is set to a predetermined minimum value MIN. The relationship between the temperature T11 sensed by the first temperature sensor 11 and the room temperature is indicated by a straight line a in FIG. 3. When it is judged that the room temperature is not less than T2 by the temperature T11 sensed by the first temperature sensor 11, the voltage of the cooling fan 6 is set to a predetermined maximum value MAX.
When it is judged that the room temperature is between T1 and T2 by the temperature T11 sensed by the first temperature sensor 11, the voltage of the cooling fan 6 is controlled in proportion to the room temperature. When it is judged that the room temperature reaches T3 by the temperature T11 sensed by the first temperature sensor 11, it is judged that the temperature is abnormal, thereby performing shut-down processing. In the shut-down processing, the power to the light source lamp for backlight is shut down, and control of the cooling fan 6 based on the temperature T11 sensed by the first temperature sensor 11 is carried out.
More specifically, when the temperature (the straight line a) T11 sensed by the first temperature sensor 11 is not less than a first shut-down temperature TS11, as shown in FIG. 3, shut-down processing is performed. When a temperature (a straight line b) T12 sensed by the second temperature sensor 12 is not less than a second shut-down temperature TS12, shut-down processing is performed. Further, when a temperature (a straight line c) T13 sensed by the third temperature sensor 13 is not less than a third shut-down temperature TS13, shut-down processing is performed.
As apparent from FIG. 3, each of the shut-down temperatures TS11, TS12, and TS13 is set such that the shut-down processing is performed when the ambient temperature of the main body of the liquid crystal projector (room temperature) is around 40° C.
In a case where the main body of the liquid crystal projector is arranged in a narrow space, when at least a part of an exhaust hole or a suction hole in the main body of the liquid crystal projector is filled up, for example, the exhaust hole or the suction hole in the main body of the liquid crystal projector is covered with a sheet-shaped object, the flow of air by the cooling fan 6 gets worse, so that the temperature inside the main body rises. When the air does not flow well, the liquid crystal panel, the light source lamp for backlight, and so forth are rapidly heated up irrespective of the fact that the cooling fan is driven.
The second temperature sensor 12 for measuring the ambient temperature of the liquid crystal panel does not adhere to the liquid crystal panel and is arranged at a position slightly apart therefrom. The third temperature sensor 13 for measuring the ambient temperature of the light source lamp for backlight is also arranged at a position slightly apart from the light source lamp for backlight. Therefore, at least a part of the exhaust hole or the suction hole in the main body of the liquid crystal projector is filled up. Even if the liquid crystal panel, the light source lamp for backlight, and so forth are rapidly heated up, heat is transmitted to the temperature sensors 12 and 13 with a time difference, so that shut-down processing is not immediately performed. Accordingly, components which are particularly weak in heat, for example, the liquid crystal panel are damaged.
Specifically, when at least a part of the exhaust hole or the suction hole in the main body of the liquid crystal projector is filled up, the respective temperatures of the liquid crystal panel and the light source lamp rapidly rise. Correspondingly, the respective temperatures sensed by the temperature sensors 12 and 13 for sensing their ambient temperatures also rise, as indicated by straight lines b1 and c1 in FIG. 4. However, heat generated by the liquid crystal panel and heat generated by the light source lamp are not immediately transmitted to the temperature sensors 12 and 13, respectively. Therefore, it takes much time until the temperatures sensed by the temperature sensors 12 and 13 respectively reach the corresponding shut-down temperatures TS12 and TS13, so that the timing of performing the shut-down processing is delayed. Accordingly, the components which are particularly weak in heat, for example, the liquid crystal panel are damaged.